Click here to get the job totals.
Download the data.
Import the data into some type of database, and then using the month() function grab all of the december data.
Now export that into a spreadsheet so you can work with it.
See the second column that has the actual jobs data in it?
Copy it to the third column and offset the row so you can subtract the 1939 data from the 1940 data as I show in that picture.
Then create a jobs column where you do the calculation.
Very simple process, or if you have the time you can type it in or cut and paste it.